Vanadium complexes have been reported to have therapeutic properties. See, e.g., C. E. Heylinger et al., Science 227:1474, 1985; Y. Shechter, Diabetes 39:1, 1990; C. Orvig et al., Metal Ions in Biol. Syst. 31:575, 1995); U.S. Pat. No. 5,527,790 by McNeill et al.; PCT published application WO 93/06811; C. Djordjevic, Metal Ions Biol. Syst. 31:595, 1995; T. F. Cruz et al., Mol. Cell. Biochem. 153:161, 1995; H. Thompson et al., Carcinogenesis 5:849, 1984; C. Djordjevic et al., J. Inorg. Biochem. 25:51, 1985; PCT published application WO 95/19177; U.S. Pat. Nos. 5,583,242 and 5,565,491; P. Caravan et al., J. Am. Chem. Soc. 117:12759, 1995; Y. Sun et al., Inorg. Chem. 35:1667, 1996; and PCT published application WO 95/20390.
However, there remains a need in the art therapeutic agents having enhanced efficacy, stability, and/or ease of synthesis, etc. The present invention is directed to meeting this need and provides additional related advantages as disclosed herein.